1. Field of the Invention
Embodiments of the present invention generally relate to downhole tools. More particularly, embodiments relate to a downhole tool having one or more frangible and/or decomposable disks for sealing off a wellbore.
2. Description of the Related Art
Bridge plugs (“plugs”) and packers are typically used to permanently or temporarily isolate two or more zones within a wellbore. Such isolation is often necessary to pressure test, perforate, frac or stimulate a section of the well without impacting or communicating with other zones within the wellbore. After completing the task requiring isolation, the plugs and/or packers are removed or otherwise compromised to reopen the wellbore and restore fluid communication from all zones both above and below the plug and/or packer.
Permanent (i.e., non-retrievable) plugs are typically drilled or milled to remove. Most non-retrievable plugs are constructed of a brittle material such as cast iron, cast aluminum, ceramics or engineered composite materials which can be drilled or milled. However, problems sometimes occur during the removal of non-retrievable plugs. For instance, without some sort of locking mechanism to hold the plug within the wellbore, the permanent plug components can bind upon the drill bit, and rotate within the casing string. Such binding can result in extremely long drill-out times, excessive casing wear, or both. Long drill-out times are highly undesirable as rig time is typically charged by the hour.
Retrievable plugs typically have anchors and sealing elements to securely anchor the plug within the wellbore in addition to a retrieving mechanism to remove the plug from the wellbore. A retrieval tool is lowered into the wellbore to engage the retrieving mechanism on the plug. When the retrieving mechanism is actuated, the slips and sealing elements on the plug are retracted, permitting withdrawal of the plug from the wellbore. A common problem with retrievable plugs is that accumulation of debris on the top of the plug may make it difficult or impossible to engage the retrieving mechanism. Debris within the well can also adversely affect the movement of the slips and/or sealing elements, thereby permitting only partial disengagement from the wellbore. Additionally, the jarring of the plug or friction between the plug and the wellbore can unexpectedly unlatch the retrieving tool, or relock the anchoring components of the plug. Difficulties in removing a retrievable bridge plug sometimes require that a retrievable plug be drilled or milled to remove the plug from the wellbore.
Other plugs have employed sealing disks partially or wholly fabricated from brittle materials that can be physically fractured by dropping a weighted bar via wireline into the casing string to fracture the sealing disks. While permitting rapid and efficient removal within vertical wellbores, weighted bars are ineffective at removing sealing solutions in deviated or horizontal wellbores. On occasion, the physical destruction of the sealing disks does not restore the full diameter of the wellbore as fragments created by the impact of the weighted bar may remain lodged within the plug or the wellbore. The increased pressure drop and reduction in flow through the wellbore caused by the less than complete removal of the sealing disks can result in lost time and increased costs incurred in drilling or milling the entire sealing plug from the wellbore to restore full fluid communication. Even where physical fracturing of the sealing disks restores full fluid communication within the wellbore, the residual debris generated by fracturing the sealing disks can accumulate within the wellbore, potentially interfering with future downhole operations.
There is a need, therefore, for a sealing solution that can effectively seal the wellbore, withstand high differential pressures, and quickly, easily, and reliably removed from the wellbore without generating debris or otherwise restricting fluid communication through the wellbore.